Process of purifying viscose solutions



Patented July 31, 1934 NITE S ATES? O C enocsssfor rnnismevrscose; SOLUTIONS. v ,Waldemar O. Mit 'scherling f l iridgeport, Conn, assignor to The Pacific Lumber Company,

Scotia, Calif.,a'corp 0ration of Maine No Drawing. -Application August 13, 1927',

r alli 2 6. r a 18 Cla ims (crate-190 This invention relates to amethod of purifying:

. 10 that the process described 'herein'is particularly.

advantageous where the cellulose is derived from the wood and bark of theredwood tree. V j It-has been found that if an amphoteric. metal either in the metallic state or in combination, :be,

5 added to the alkalinesolution' which is to'be spun,

that the amphoteric metal will. react with the alkaline solution to give -'a metallic hydroxid and this further reacts to form an alkali metal salt of theamphoteric metal, and that this'reacts further .12 with certain of the organic constituents of the solution to give; a gelatinous precipitate. For example, if v theusual viscosesolution is used, and an amphoteric metal such as aluminum is-added to this solution, a gelatinous precipitate will; be formed whichwill carry down with it certain of the impuritiesand from which the ,clear solution may be separated by any-desired means such as filtration or by subjectingit to centrifugal action. Simultaneously, with the formation by the metal licaluminum of the sodium aluminate, hydrogen gas is evolved. H V V ,If aluminum is employedthe amount of aluminum which may be used varies according .to the amountot impurities in the spinning solution and also according to the degree to which these im puritiesare desired to ;be eliminated.- It has been found that an amount ofaluminum between onehalf of one per cent. and two per cent. byweight calculated on the cellulose content of the solution is satisfactory. g 1; 7

Although in the above example -I.have setforth the use; of aluminum as the. amphoteric met'al Which is to be employed success can be similarly obtained by adding to the spinning solution other amphoteric metals either combinedor uncombined and I have obtained satisfactory results by using zinc, zinc hydroxid, aluminum hydroxid, sodium zincate and sodium aluminate. The purification resulting is essentially the same no matter which of these materials is used. I prefer, however, to use zinc hydroxid or metallic aluminum.

By subjecting the spinning solution to the action of an amphoteric metal hydroxid, the remaining solution not only is purified but it has also been found is not subject to as rapid deterioration as theunpurified solution. This is probably 'duetothe precipitation of someof the usual decomposition products attendant upon xanthation. The lustre of the rayon filaments made from this purified solution diifers optically from rayon madefrom unpurifiedviscose solutions in that it. does not reflect light from the surface so glaringly; but instead there is a translucent effect very similar'to the appearance of silk from the silkwormv cocoon. i r

' The degree ofpurificationthus effected may be controlledcbypthe' quantity of the amphoteric metal which is permitted to act on the solution. Iftheoamphoteric metal be finely divided its .0 action will be more rapid than ifcthe metal be used inlarger particles. In case finely powdered metal is employed it is of course necessary to guard suitably against too great a rise of temperature, say by adding the purifying agent-l slowly or by refrigeration... l

. The above described reaction when carried out produces a precipitate of agelatinous or slimy nature containing the impurities and. this pre'. cipitate forms a layer which canbe removed, thoughwith somedifiiculty, by means of a filter or by the action .ofacentrifuge or othersimilar device. A device which has proved particularly successful inseparating these impuritiesv from the spinning solution may consist of an. ordinary. cylindrical centrifugal separator containing a liningof amphoteric material such for example, as.metallic aluminum or zinc. For example,a removable aluminum shell, preferably. splitso that it will tightlyconform to the. inside of the cylinder 'may advantageously be placed. within a centrifuge of any usual'type. Inusing a centrifugalseparator in the practice of my-process the spinning solution may be allowed to enter through the bottom of the cylinder and by the action of centrifugal forceis whirled, in contact with the amphoteric metal, which is used as alining, and

is withdrawn from the upper end. of the cylinder. 'I'he centrifugalaction of the process and the contact of the solutionwith the amphoteric metal gives rise to a chemical reaction between the materials in the spinning solution and the material of which the lining of the cylinder is formed in a manner similar to that which would take place if a finely powdered metal or compound of 1 such metal were added to the spinning solution in a stationary container. The sludge formed on the shell by the action of the metal with the impurities in the spinning solution will gradually be carried toward the discharge end of the centrifugal machine and is taken away through an outlet separate from that used to carry away the purified spinning solution.

Although I have set forth the preferred method of practicing my invention, it is to be understood that changes may be made in the steps of the process and the materials employed without departing from the spirit of my invention or the scope of the subjoined claims.

I claim:

1. The method of purifying an alkaline cellulose solution which comprises effecting the reaction of an amphoteric metal hydroxid with a constituent of such solution adapted to combine with the amphoteric metal to form a precipitate containing the impurities and removing said precipitate therefrom while the solution is still alkaline.

2. The method of purifying an alkaline cellulose solution which comprises efiecting the reaction of an amphoteric metal which will give an hydroxid with constituents of such solution adaptedto combine with the amphoteric metal to form a precipitate containing the impurities and removing said precipitate therefrom while the solution is still alkaline.

'3. The method of purifying an alkaline cellulose solution containing a compound of an alkali metal which comprises effecting the reaction of such alkali metal and an amphoteric metal hydroxid and an organic constituent of the solution, and removing a product of such reaction therefrom while the solution is still alkaline, which product contains impurities formerly in the cellulose solution.

4. The method of purifying a cellulose solution containing a compound of an alkali metal which comprises effecting the reaction of such alkali metal compound andaluminum and an organic constituent of. the solution and removing the product of such reaction therefrom.

5. The method of purifying an alkaline cellulose solution containing a compound of sodium which comprises effecting the reaction of the sodium and an amphoteric metal hydroxid and an organic constituent present as an impurity in thesolution'and removing the resulting precipitate containing said impurity therefrom while the solution is still alkaline.

6. The method of purifying a cellulose solution containing a compound of sodium which comprises eifecting the reaction of the sodium and metallic aluminum and organic constituents of the solution and removing a product of such reaction therefrom.

7. In a process of purifying alkaline cellulose solutions the stepsof reacting upon a cellulose solution containing a compound of an alkali metal with an amphoteric metal hydroxid adapted to produce a gelatinous precipitate therewith said gelatinous precipitate being adapted to remove impurities from said solution, and separating said precipitate and said impurities from said solution while the solution is still alkaline.

8. In a'process of purifying alkaline cellulose solution the steps of reacting upon a cellulose solution containing a compound of sodium with an amphoteric metal hydroxid adapted to produce a gelatinous precipitate therewith, said gelatinous precipitate being adapted to remove impurities from said solution, and separating said precipitate and said impurities from said solution while the solution is still alkaline.

9. The herein described process comprising reacting upon an alkaline viscose with an amphote'ric metal hydroxid and separating the resulting precipitate containing impurities formerly present in said viscose therefrom while the solution is still alkaline.

10. The herein described process comprising reacting upon viscose with aluminum, and separating the resulting precipitate containing impurities formerly present in said viscose therefrom.

11. The method of purifying a viscose solution which comprises effecting the reaction of an amphoteric metalwith constituents of such solution under theinfluence of centrifugal force to separate impurities present in said solution therefrom, and removingv said impurities.

12. The method of purifying a viscose solution which comprises effecting the reaction of aluminum with constituents of such solution under the. influence of centrifugal force to separate impurities present in said solution therefrom, and removing said impurities.

13. The method of purifying a viscose solu-- tion which comprises effecting the whirling of the solution in contact with a surface of an amphoteric metal.

141. The method of purifying a viscose solution which comprises effecting the whirling of the solution by a centrifugal action in contact with an aluminum surface.

15. The method of purifying-an alkaline viscose solution which comprises effecting the reaction of an amphoteric metal with sodium and organic constituents present in the solution to produce a gelatinous precipitate and removing said precipitate therefrom while the solution is still alkaline.

16. The method of modifying the lustre of viscose rayon which-comprises removing a portion of the lustre producing content of the alkaline viscose solution to be spun into rayon by the reaction of an amphoteric metal hydroxide upona constituent of such solution and separating the resulting product while the solution is still alkaline. i

1'7. In the manufacture of viscose products the step comprising treating alkaline viscose solution with metallic aluminumprior to spinning.

' 18. In the manufacture of viscose products the method of purifying alkaline viscose solution comprising treating said solution prior to spinning with afinely divided metallic metal which is rapidly dissolved in alkali with liberation of hydrogen, dissolution of said metal destroying sulfur-compound impurities in the viscose solution. I

WALDEMAR O. MITSCHERLING. 

